The synthesis and in vitro evaluation of a series of amino acids is proposed, with the primary goal being to develop a diagnostically useful pancreas-imaging agent. An intensive investigation of the transport properties of a large group of neutral amino acids will be conducted for determination of the chemical structures that confer pancreas specificity. Both D- and L- forms of the amino acids will be screened for determination of stereoselectivity in the uptake phenomenon. The amino acids will be evaluated initially in vivo in rats and, to a limited extent, in dogs and monkeys. This assay will be facilitated by isotopic labeling of these amino acids with 3H, 14C, or 125I. In vitro assays will be developed for dogs and monkeys to permit screening of these amino acids with these animals.